MIC2185YQS Micrel Inc, MIC2185YQS Datasheet - Page 8

• Manufacturer Part Number: MIC2185YQS
• Description: SO-16 Low Vin Synchronous Buck PWM Control IC ( )
• Manufacturer: Micrel Inc

Specifications of MIC2185YQS

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 440kHz
• Duty Cycle: 95%
• Voltage - Supply: 2.9 V ~ 14 V
• Buck: No
• Boost: Yes
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 16-QSOP
• Frequency-max: 440kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-2162; MIC2185YQS

MOSFET, Q2. Current flows through the MOSFET because
its voltage drop is less than diode D1. The MOSFET remains
on until the end of the switching cycle. There is another
non-overlap time delay between the turn-off of the high side
MOSFET and the turn-on of the low side MOSFET at the
beginning of the next switching cycle.
The description of the MIC2185 controller is broken down
into 6 basic functions.
MIC2185
• Control Loop
• Current Limit
• MOSFET gate drive
• Reference, Enable & UVLO
• Oscillator & Sync
• Soft Start
• PWM Operation
• SKIP Mode Operation
V
IN
V
DD
EN/UVLO
FREQ/2
COMP
SYNC
VREF
SKIP
VDD
SS
15
11
10
7
2
3
4
8
V
V
REF
DD
Figure 2. MIC2185 Skip Mode Block Diagram
Osc
Control
C
DECOUP
SGND
Current Reset
S
On
GND
V
Limit Comparator
5
IN
Bias
A
Skip Current
1
Comparator
8
Hysteresis
V
V
Control Loop
PWM and SKIP modes of operation
The MIC2185 can operate in either PWM (pulse width modu-
lated) or skip mode. The efficiency of the boost converter can
be improved at lower output loads by manually selecting the
skip mode of operation. The potential disadvantage of skip
mode is the variable switching frequency that accompanies
this mode of operation. The occurrence of switching pulses
depends on component values as well as line and load con-
ditions. PWM mode is the best choice of operation at higher
output loads. In skip mode, current through the inductor can
settle to zero, causing voltage ringing across the inductor.
PWM mode has the advantages of lower output ripple volt-
age and higher efficiencies at higher output loads. Another
advantage of the synchronous PWM mode of operation is
that the inductor current is always continuous, even at zero
output current. This reduces parasitic ringing that occurs
1%
REF
DD
50mV
1.245V
V
REF
C
IN
P
GND
P
P
GND
GND
V
16
OUTP
14
OUTN
13
CSH
9
PGND
12
FB
6
IN
P
L1
R
Q1
SENSE
Q2
D1
C
OUT
R1
R2
V
OUT
October 2005